Omega-3 fatty acids are considered essential fatty acids, which means that they are essential to human health but cannot be synthesised by the human body. For this reason, omega-3 fatty acids must be obtained through the diet.
The European Pharmacopoeia defines the omega-3 fatty acids as the following acids (see for example Monograph no. 1912, Fish Oil, Rich in Omega-3-Acids): alpha-linolenic acid (C18:3 n-3; ALA), moroctic acid (C18:4 n-3), eicosatetraenoic acid (C20:4 n-3), eicosapentaenoic (timnodonic) acid (C20:5 n-3; EPA), heneicosapentaenoic acid (C21:5 n-3), docosapentaenoic (clupanodonic) acid (C22:5 n-3) and docosahexaenoic (cervonic) acid (C22:6 n-3; EPA). Omega-3 fatty acids with chain-length of 20 and above are called long-chain omega-3 fatty acids. ALA is common in a number of vegetable oils. C18:4 n-3 is available from fish oils, as well as from some vegetable oils. Once eaten, the body can to some extent convert ALA and C18:4 n-3 to the long-chain omega-3 fatty acids, including EPA and DHA. However, fish oil and other marine oils are known to be the best source of these omega-3 fatty acids. Long-chain omega-3 fatty acids can also be obtained via fermentation of single cell oils (microbial oils), and research projects aim at producing EPA and DHA via gene-modified terrestrial plants.
Omega-3 fatty acids have been demonstrated to reduce the risk of coronary heart disease as well as having a positive effect on children's development, as well as on the skin. Results have also been disclosed indicating the positive effect of these fatty acids on certain mental illnesses, autoimmune diseases and joint complaints. There are therefore many reasons for considering taking fish oil as a valuable dietary supplement, including the long-term effect which this dietary supplement is now thought to have.
However, fish oils and especially concentrates of omega-3 fatty acids are very susceptible to oxidation. Oxidation limits the use of such products in food applications, and also limits oral administration of omega-3 containing nutritional supplements, except where the supplements are encapsulated.
Microencapsulation is a way of formulating omega-3 oils for food applications. However, microencapsulated products are relatively expensive, the encapsulation material often takes up more volume than the oil, so that the total volume becomes impractical to handle, and also there might be doubts whether the encapsulation material prevents the valuable omega-3 fatty acids from being absorbed in the intestinal tract.
An alternative to microencapsulation is the use of antioxidants in the oil to slow down oxidation. Most antioxidants interfere with the propagation of lipid oxidation by donating a hydrogen atom to, and thereby inactivating, chain-carrying peroxyl radicals and/or alkoxyl radicals. Hence, after breaking the chain reaction of lipid peroxidation, an antioxidant is itself converted to a radical. To be effective, the antioxidant radical has to be sufficiently stable so as to react slowly with the lipid substrate and rapidly with lipid peroxyl radicals and/or alkoxyl radicals. Several natural and synthetic compounds fulfil this condition and are widely used for preserving polyunsaturated fatty acids (PUFA) from oxidative deterioration. Even though a number of synthetic antioxidants have been extensively used for the stabilization of foods, much interest has developed in the use of naturally occurring antioxidants because of the adverse attention received by the synthetic antioxidants and because of the worldwide trend to avoid or minimize the use of synthetic food additives.
Tocopherols are among the most important lipid-soluble natural antioxidants, and appear to be the major physiological scavengers of free radicals inside human membranes and plasma lipids. The fact that these compounds are naturally occurring lipid-soluble antioxidants make them particularly useful in combination with marine oils, having high amounts of PUFA, intended for human consumption (Free radical biology & medicine, 2005, vol. 38, page 78-84; J. Chem. Soc., Perkin Trans. 2, 1998).
Another example of antioxidants commonly used in combination with marine oils are rosemary extracts. The antioxidant potential of such an extract has previously been tested on cod liver oil and has been shown to have significantly higher antioxidant effect compared with seven other naturally occurring antioxidants (Journal of Aquatic Food Product Technology; vol. 14; 2005; page 75-94). Further, a mixture of α-tocopherol and rosemary extract has previously been shown to exert very strong antioxidant activity in sardine oil, where their combination not only inhibited the formation of hydroperoxides much more effectively than when present separately but the activity of tocopherol was retained for a longer period of time (Yukagaku 1994, vol. 43, no 2, page 109-115).
Ascorbyl palmitate is an ester formed from ascorbic acid and palmitic acid. In addition to its use as a source of vitamin C, it is also commonly used as an antioxidant food additive. The compound is difficult to dissolve in oil formulations, and it is therefore common to add lecithin to the antioxidant preparation in order to solubilise the ascorbyl palmitate (EP612346). Even though lecithin is commonly regarded as a well-tolerated and non-toxic surfactant, lecithin may contain traces of proteins and for this reason has to be declared as a potential allergen in nutritional supplements. Producers and distributors prefer to avoid components that might act as allergens.
In addition to traditional and cultural reasons for consuming tea, a renewed interest has been fuelled by the discovery of strong antioxidant properties provided by tea prepared from Camellia Sinensis leaves (green tea). Such an antioxidant effect has primarily been attributed to the polyphenol content of the tea leaves, commonly known as tea catechins. Said catechins are water-soluble and therefore not easily dissolvable in oil formulations. In order to make these strong antioxidants lipid-soluble, it has been suggested to derivatise part of the phenols with fatty acid (WO07021789). An unwanted side effect of derivatising these compounds with fatty acids is that the intestinal absorption of these compounds increases significantly. Polyphenols from green tea are generally not absorbed into the body, and the increased absorption of these compounds add a problem from a regulatory point of view.
Even though a number of antioxidants and various combinations thereof have been disclosed (e.g. U.S. Pat. No. 5,102,659), there is still a need for additional antioxidant compositions having improved characteristics.